We May Have Already Detected Signs of Alien Microbes on Saturn’s Moon Enceladus

According to a new study, microbes like those found in Earth’s deep ocean could potentially thrive in the underground ocean of Saturn’s icy moon Enceladus. Both molecular hydrogen (H2) and methane (CH4) already have been detected in the plume. Researchers have shown that Methanothermococcus okinawensis, a methanogenic archaeon first isolated from a deep-sea hydrothermal vent on the western Pacific Ocean, can produce methane under conditions known to exist on Enceladus.

Enceladus as viewed from NASA’s Cassini spacecraft. It is Saturn’s sixth largest moon, only 157 miles (252 km) in mean radius, but it’s one of the most scientifically compelling bodies in our solar system. Hydrothermal vents spew water vapor and ice particles from an underground ocean beneath the icy crust of Enceladus. This plume of material includes organic compounds, volatile gases, carbon dioxide, carbon monoxide, salts, and silica. With its global ocean, unique chemistry and internal heat, Enceladus has become a promising lead in our search for worlds where life could exist. Image: NASA.gov

Methanothermococcus okinawensis is a thermophilic, methane-producing archaeon. It was first isolated from deep-sea hydrothermal vent on the western Pacific Ocean. It is strictly anaerobic (survives without oxygen) and reduces carbon dioxide with hydrogen (both observed in Enceladus’s atmosphere by the Cassini spacecraft) to produce methane as a waste product. It can also use formate. Cassini also detected traces of methane in the icy moon’s plumes. Researchers say “there’s a chance that some of it may have come from this kind of microbe”.

Simon Rittmann at the University of Vienna in Austria, who led the research, says “The conditions we mimicked in the lab are as close as possible to those inferred from Cassini on Enceladus. It’s likely this organism could be living on other planetary bodies.”

The researchers introduced a few species of microbes to a wide range of possible scenarios that might be found on Enceladus. One of the species, Methanothermococcus okinawensis, fared the best under Enceladus conditions. The microbe continued to thrive at temperatures and pressures likely found in the moon’s oceans: 0 to 90 degrees Celsius, and up to 50 Earth atmospheres. It even survived when the researchers introduced unfriendly chemicals like ammonia (NH3) and carbon monoxide (CO), which also found on the moon.

To clarify things, the researchers don’t claim the source of methane on Enceladus is biological. They have shown that some Earth microbes even could thrive under the conditions found on the Saturn’s icy moon. Rittmann says “From an astronomical perspective, future missions to Enceladus or other icy moons should be equipped to be able to detect methanogenic biosignatures related to methanogens, like certain lipids or ratios of certain carbon isotopes”.

Unfortunately, currently there are no planned Enceladus missions by NASA or any other space agency, in the near future. But, a private program founded by billionaire tech investor Yuri Milner to hunt for alien life and help explore the cosmos is considering launching a mission that would fly through the plume of water vapor and other material emanating from Enceladus’ south polar region.

Enceladus: a hot spot in the search for extraterrestrial life

Enceladus was discovered by the British astronomer and composer (of German and Czech-Jewish origin) William Herschel on August 28, 1789. It is named after the giant Enceladus of Greek mythology. Until NASA’s Voyager 1 and Voyager 2 spacecrafts passed nearby in the early 1980s, little was known about the icy moon. In 2005, the Cassini spacecraftNotes 1 started multiple close flybys of Enceladus, revealing its surface and environment in greater detail.

One of its flybys, in 2008, the spacecraft get really close (50 km) to the surface, passed through the plumes extending from its southern geysers, detecting water, carbon dioxide and various hydrocarbons.

On April 3, 2014, nearly ten years after Cassini entered Saturn’s orbit, NASA reported evidence of a large salty internal ocean of liquid water in Enceladus. The presence of an internal salty ocean in contact with the moon’s rocky core, places Enceladus “among the most likely places in the Solar System to host alien microbial life”. On June 30, 2014, NASA celebrated ten years of Cassini exploring Saturn and its moons, highlighting the discovery of water activity on Enceladus among other findings.

In September 2015, NASA announced that gravitational and imaging data from Cassini were used to analyze the librations of Enceladus’ orbit and determined that the moon’s surface is not rigidly joined to its core, concluding that the underground ocean must therefore be global in extent.

On October 28, 2015, Cassini performed another close flyby, coming within 49 km (30 mi) of the surface, and passing through the icy plume above the south pole.

Enceladus is a relatively small satellite composed of ice and rock. Its diameters, calculated from images taken by Cassini’s ISS (Imaging Science Subsystem) instrument, are 513 km between the sub- and anti-Saturnian poles, 503 km between the leading and trailing hemispheres, and 497 km between the north and south poles. It is only one-seventh the diameter of Earth’s Moon.

Notes

The Cassini-Huygens mission, commonly called Cassini, was a collaboration between NASA, the European Space Agency (ESA), and the Italian Space Agency (ASI) to send a probe to study the planet Saturn and its system, including its rings and natural satellites. The Flagship-class robotic spacecraft comprised both NASA’s Cassini probe, and ESA’s Huygens lander which landed on Saturn’s largest moon, Titan. Cassini was the fourth space probe to visit Saturn and the first to enter its orbit. The craft were named after astronomers Giovanni Cassini (8 June 1625 – 14 September 1712) and Christiaan Huygens (4 April 1629 – 8 July 1695).